The proposed research is designed to add additional information on the fine structure of the substantia gelatinosa. The methods to be employed are morphometric analysis, counts and classification of cells, numbers and types of synaptic terminals and number and types of synaptic contacts. These methods will be used on normal material and on spinal cord segments acutely and chronically deprived of neuronal input from dorsal root ganglia and from ascending and descending intraspinal fibers. A Golgi method as modified by Fairen, Peters and Saldanha 1977, will be used to distinguish between small dendritic and axonal profiles. Tritiated leucine and horseradish peroxidase will be injected into dorsal root ganglia and spinal gray matter to identify sources of synaptic terminals.